Psychrophilic and psychrotrophic microorganisms in food and water: Qualitative and quantitative culture; Molecular identification (sequencing).
Alteration of foods maintained at refrigeration temperatures occurs from psychrophilic and psychrotrophic microorganisms, with the ability to multiply at low temperatures. In addition to the deterioration of food, the growth of microorganisms can have pathogenic and toxigenic effects for humans.
Psychrophilic microorganisms are those whose optimum growth temperature is low, approximately 15°C or lower, and have a maximum growth temperature of approximately 20°C. These microorganisms grow at refrigeration temperatures and are found in environments where the temperature is always below 15 to 20°C. They are present in arctic and alpine soils, high latitudes, ice formations and deep oceanic waters. Most psychrophilic organisms are bacteria or archeas, but also fungi and some species of yeast. Most of the psychrophilic bacteria found in food are Gram negative, and include the genus Aeromonas, Alcaligenes, Flavobacterium, Pseudomonas, Serratia and Vibrio. Gram-positive microorganisms include species of Bacillus, Clostridium and Micrococcus.
Secondly, psychrotrophic microorganisms, also known as facultative or psychrotolerant psychrophiles, are microorganisms whose optimum growth temperature is in the mesophilic range, above 15 to 20°C, closer to room temperature, but they can also multiply at temperatures below 7°C. These microorganisms grow in environments where the temperature fluctuates, being adapted to large oscillations. They are the main microorganisms involved in the deterioration of refrigerated foods. These microorganisms are brought into the food from their mesophilic habitats and continue to grow in the refrigerated environment, albeit more slowly. Within the psychrotrophic microorganisms, bacteria are the main responsible for the deterioration of chilled foods of animal origin, while molds and vegetables are in fruits and vegetables.
Products of animal origin, mainly raw or cooked meats, fresh or cooked seafood, dairy products and butter, are altered during storage at temperatures higher than those of freezing due to bacterial growth. In addition to aerobic microorganisms, the use of vacuum or modified atmosphere in the packaging of raw or processed meats, fish, and other foods favors the growth of strict anaerobic microorganisms and facultative anaerobes, mainly psychrophilic and psychrotrophic species of the genus Clostridium.
Among the psychrotrophic bacteria include Aeromonas, Acinetobacter, Alcaligenes, Psychrobacter, Brochothrix, Enterobacter, Microbacterium, Moraxella, Carnobacterium, Shewanella, Campylobacter, Yersinia, Pseudomonas, Serratia, Achromobacter, Streptococcus, Leuconostoc, Pediococcus, Lactobacillus, Lactococcus, Flavobacterium, Alcaligenes , Klebsiella, Escherichia, Proteus, Hafnia and Clostridium. In addition, from food spoilage, certain human pathogens can grow at refrigeration temperatures, such as Clostridium botulinum type E and non-proteolytic types B and F, Listeria monocytogenes, Campylobacter jejuni, Yersinia enterocolitica, some strains of Bacillus cereus and of Escherichia coli, and Aeromonas hydrophila.
Fungi predominate in the deterioration of chilled foods when low water activity, high acidity or packaging conditions are selected for growth on bacteria in food. Psychrotrophic fungi are usually isolated from refrigerated products of animal products, fresh fruits and vegetables, and ready-to-eat foods. The genera of filamentous fungi that have psychrotrophic species include Alternaria, Aspergillus, Botrytis, Cladosporium, Fusarium, Geothricum, Monascus, Mucor, Penicillium, Rhizopus and Trichothecium. Among the yeast genera involved are Candida, Debaryomyces, Saccharomyces, Torulopsis.